I know your neighbor teams in Steinberg, regarding all other products than Dorico, are too hesitate to prepare compatibility works with new major system versions even though developer preview builds are available.
Developer preview builds are released for you software developers to do the compatibility preparations. It’s not a good idea to ignore these builds. Thus, I am wondering you Dorico team could be aware of such essense.
P.S.: AFAIK, macOS Sierra ditched most Snow-Leopard APIs popular among those softwares used in audio industry. Please do not hesitate on starting troubleshooting compatibility issues, because this will be a time-consuming big work for this year.